1. Field of Invention:
This invention relates to a diagnostic apparatus for optically performing subtractions of optical images which are taken by use of a radiation source, and more particularly to a diagnostic apparatus in which subtractions on a series of optical images of an object are optically carried out between them by utilizing electrooptic effect devices.
2. Description of Prior Art:
In general, an X-ray diagnostic apparatus is known from, e.g., U.S. Pat. No. 4,204,225 and 4,204,226 both issued on May 20, 1980, that a plurality of transmission images of an object, e.g., blood vessels of a patient are first taken by an X-ray projection and then subsequently converted into electric digital signals which are temporarily stored in respective memories. Thereafter digital subtraction is carried out by utilizing the stored digital image signals, whereby the subtracted images of the blood vessels are observed in a TV monitor for diagnostic purposes.
In the above-mentioned known X-ray diagnostic apparatus, the following recent developments have been introduced so as to improve the diagnostic technique. For example, as to at angiography examination, there is digital radiography, or digital fluoroscopy into which are applied the digital processing and time subtraction technique involving mask mode subtraction, time interval difference mode subtraction and so on.
As previously described, image subtraction processing in known X-ray diagnostic apparatus is usually carried out after converting the X-ray transmission images into digital signals and storing them in memories. Accordingly plenty of processing time and a huge capacity of the memories are required to process a series of time-continuous television image signals. In other words, according to those conventional apparatus, real time processing of the digital subtraction is very difficult in practice.
Moreover the subtraction on the optical images of the object, e.g., the mask images and the contrast images, is performed after first converting them into the proper digital signals by means of a television camera, so that the density resolving power of those optical images is lowered when observed in a television monitor. As a result, there is another problem that useful subtraction image information is not available for diagnostic purposes.
It is therefore an object of the present invention to provide a diagnostic apparatus into which such a novel technical idea is introduced that a subtraction is carried out by employing electrooptic effect devices between the optical images of the object.